A level-up shifter is an essential element for input/output (IO) design that handles signals crossing from a core power supply domain to an IO power supply domain, where the IO supply voltage is higher than that of the core supply. For the full-swing GHz high speed signals, a level-up shifter that can handle rail to rail signal level and preserve duty cycle fidelity is desirable. Further, as power dissipation becomes an important factor in IC design, it is critical to reduce DC current paths. Because a level-up shifter must transfer signals from one power domain to another, short-circuit currents may still be present when driving a static DC level, particularly as the difference between core and IO supply grows larger.